PS + CSOM to activate/deactivate a Feature (e.g. in SharePoint Online)..

ActivateOrDeactivateFeature_PSCSOM.ps1

. .\TopOfScript.ps1

[bool]$enable = $true
[bool]$force = $false

# using the Minimal Download Strategy Feature here..
$FeatureId = [GUID]("87294C72-F260-42f3-A41B-981A2FFCE37A")

# ..and working with the web-scoped Features - use $clientContext.Site.Features for site-scoped Features
$webFeatures = $clientContext.Web.Features 
$clientContext.Load($webFeatures)
$clientContext.ExecuteQuery()

if ($enable)
{
	$webfeatures.Add($featureId, $force, [Microsoft.SharePoint.Client.FeatureDefinitionScope]::None)
}
else
{
	$webfeatures.Remove($featureId, $force)
}

try 
{
	$clientContext.ExecuteQuery()
	if ($enable)
	{
		Write-Host "Feature '$FeatureId' successfully activated.."
	}
	else
	{
		Write-Host "Feature '$FeatureId' successfully deactivated.."
	}
}
catch 
{
	Write-Error "An error occurred whilst activating/deactivating the Feature. Error detail: $($_)"
}